Proteins from the Protein Production Core produced in bacteria for crystal structure analysis will routinely be Se-Met labeled to directly enable phasing. For those produced in other hosts or initially provided by collaborators, additional approaches to phasing, such as via multiple isomorphous replacement methods as described below, will be used. The major objectives are (1) to develop crystallization and additive screens formulated specifically for protein complexes to optimize the probability of obtaining diffracting crystals and (2) to solve structures of HIV accessory/regulatory proteins using high-throughput approaches for crystallization, data collection, and structure determination. The ultimate goal is to solve the structures of HIV accessory/regulatory proteins in complexes with cellular proteins and to accomplish this by using rational approaches, as described throughout this proposal.